Technical Field
The invention relates to a synthetic pheromone composition relating to the foraging behavior of bees, to its composition and to its uses.
Introduction
Social insects perform all the tasks of colony growth and maintenance concurrently by division of labor. One view is that division of labor is an emergent property that is self-organized through the interactions of individual workers with stimuli in their environment (Page R. E., Jr. et al. PSA 2:28-298 (1990)). A division of labor emerges when individuals have different response thresholds for stimuli that release behavioral responses. The evolution of specific patterns of organization results as a consequence of selection acting on genetic variability affecting response threshold distributions of colonies.
Bees are insects of the order Hymenoptera, which feed on pollen and nectar. They constitute a group of about 20 000 species throughout the world, known taxonomically as the Superfamily Apoidea. Honey bees of the genus Apis belong to the family Apidae, a sub-group of this superfamily. Although the question of how many honey bee species exist is still debated among taxonomists, at least four species are commonly recognized: the dwarf, or midget, bee Apis florea, the giant, or rock, bee Apis dorsata, the oriental (Indian, Chinese, Japanese, etc.) bee Apis cerana, and the common (European, African, etc.) honey bee Apis mellifera. The existence of another giant bee, Apis laboriosa, has recently been confirmed.
Bees of the family Apoidea are eusocial insects, that is to say that they engage in favorable social activity. Depending on the species, a colony of bees consists of a queen, dozens to thousands of workers, and at certain seasons of the year anywhere from a few to a few-hundred drones. Among the members of the colony there is division of labor and specialization in the performance of biological functions.
Bees construct variously shaped cells to rear their brood and to store their food. In the genus Apis, general utilization of comb space is similar among the species, with honey stored in the upper part of the comb, with, beneath it, rows of pollen-storage cells, worker-brood cells, and drone-brood cells, in that order. The groundnut-shaped queen cells are normally built at the lower edge of the comb.
As an inherited behavior characteristic, all bee colonies tend to store a certain amount of honey and pollen as their food reserve. The quantity of food stored depends upon several factors, including the seasonal availability of forage, the worker population of the colony and its rate of reproduction, the capacity of the nest, etc. Another important inherited behavior characteristic lies in the colony""s natural site of comb construction. For instance, some Apis species build single comb nests in the open, while others build multiple-comb nests in dark cavities.
In honey bees, studies suggest that colony environment modulates foraging behavior. The amount of pollen stored in the comb affects the proportion of pollen foragers. More stored pollen results in less pollen foraging (Allen M. D. et al., Ann Applied Biol 44:649-656 (1956); Fewell, J. H. et al., Behav Ecol Sociobiol 30:387-393 (1992); Fewell, J. H. et al., Experientia 49:1106-1112 (1993)). The amount of young larvae also affects the proportion of foragers collecting pollen: more larvae and empty space result in more pollen foraging (Al-Tikrity W. S. et al., J Apic Res 11:9-12 (1972); Barker, R. J., J Apic Res 10:23-26 (1971); Dreller C. et al., Behav. Ecol. Sociobiol. 45:227-233 (1999); Eckert C. D. et al., Oecologia 97:248-255 (1994); Fewell, J. H. et al., Behav Ecol Sociobiol 30:387-393 (1992); Free, J. B. Anim Behav 15:134-144 (1967); Free, J. B. App Anim Ethol 5:173-178 (1979); Jaycox 1970; Todd F. E. et al., J Econ Ent 63:148-149 (1970)). Larval substances soluble in hexane releases pollen foraging (Pankiw T. et al., Behav Ecol Sociobiol 44:193-198 (1998)).
Foraging behavior and the mechanisms that regulate foraging activity are important components of social organization. Recently the honey bee proboscis extension response to sucrose has been identified as a xe2x80x9cwindowxe2x80x9d into a bee""s perception of sugar (Page R. E., Jr. et al. PSA 2:28-298 (1990)). The sucrose response threshold measured in the first week of adult life, prior to foraging age, predicts forage choice (Pankiw T. et al., Behav Ecol Sociobiol 47:265-267 (2000)). Bees with low response thresholds are more likely to be pollen foragers and bees with high response thresholds are more likely to forage for nectar. There is an associated genetic component to sucrose response thresholds and forage choice, such that bees selected to hoard high quantities of pollen have low response thresholds and bees selected to hoard low quantities of pollen have higher response thresholds.
The number of larvae in colonies also affects the number of bees foraging for pollen. Hexane extractable compounds from the surface of larvae (brood pheromone) significantly increase the number of pollen foragers (Pankiw T. et al., Behav Ecol Sociobiol 44:193-198 (1998); Pankiw T. et al., J Comp Physiol A185:207-213 (1999); Pankiw T. et al., Behav Ecol Sociobiol. 49:206-213 (2001)). Brood pheromone decreases the sucrose response threshold of bees suggesting a pheromone-modulated sensory-physiological mechanism for regulating foraging division of labor. Honey bees respond reflexively to sucrose by extending the proboscis when a sufficiently concentrated solution touches the antennae (Bitterman, M. E. et al., J Comp Psychol 97:107-119 (1983)). Brood pheromone significantly decreased response thresholds as measured in the proboscis extension response assay (PER-RT assay), a response associated with pollen foraging (Page R. E. et al., Anim Behav 50:1617-1625 (1995)). Pollen foragers have lower sucrose response thresholds than do nectar foragers (Page R. E. et al., J Comp Physiol A 182:489-500 (1998)). Water foragers have the lowest response thresholds to sucrose as pre-foragers, pollen foragers have the next lowest response thresholds, followed by nectar foragers, and foragers returning empty have the highest response thresholds (Pankiw T. et al., Behav Ecol Sociobiol 47:265-267 (2000)).
Response thresholds to sucrose are also plastic, modulated by nutritional status and previous foraging experience. Response thresholds are lower in bees fed lower quality sucrose solutions for 24 hours than bees fed high quality solutions. Previous foraging experience with low or high quality sucrose solutions modulates response thresholds in the same way. Genotype places a constraint on phenotypic response threshold plasticity such that strains of bees that were selected to hoard high or low quantities of pollen (Page R. E. et al., Anim Behav 50:1617-1625 (1995)), when fed high or low quality sucrose solutions have response thresholds that are proportionately modulated, however strain differences are maintained at all concentrations fed.
Reports have suggested that nectar foraging may be induced by nurse bees by the secretion of a substance inhibiting pollen foraging in workers. (Camazine, S. Behav Ecol Sociobiol. 32:265-272 (1993)). By this proposed mechanism, foraging behavior is controlled by the indirect effects of nurse bees producing a pollen-foraging inhibitor, with the amount of inhibitor available to feed to foragers depending on the amount of pollen stored and the number of larvae that must be fed. In a recent book on honey bee social organization, this explanation is supported as the way bees regulate pollen collection. (Seeley T. D. The social physiology of honey bee colonies.xe2x80x9cHarvard University Press, Cambridge Mass.xe2x80x9d (1995)).
The direct value of honey bees as pollinators is valued at more that $14 billion annually in the United States. However, commercial honey bee populations are continually dwindling due to recently imported parasites and pathogens, and due to the invasion of the Africanized Honey Bee.
According to Morse et al., the value of the rental bee colony business alone in 1999 was close to $6 billion in the United States, with the leading crops utilizing such services comprising apple, melons, alfalfa seed, plum/prune, avocado, blueberry, cherry, vegetable seed, pear, cucumber, sunflower, cranberry and kiwi. This value does not include the value of spillover pollination, where the bees are released to pollinate a crop for free for the benefit to the beekeeper of collecting honey.
Parasitic mite and mite-related diseases have caused the death of most wild honey bees in the United States, on the order of 95 to 98 percent of the wild honey bee colonies, and left commercial colonies at risk. In particular, the Varroa mite represents a great threat to beekeeping, and beekeepers have only one registered chemical (Apistan) to control Varroa mites. In Europe, mites have already become resistant to that chemical.
The colonies kept by commercial beekeepers have also suffered serious losses. Research on the biology and control of bee foraging may make it possible for the industry to compensate with fewer colonies and still provide needed pollination of crops. Some 90 different crops-ranging from apples to zucchini and cantaloupes to cucumbersxe2x80x94depend on honey bee pollination. To some extent, other insects will pollinate specific crops. However, no insect is as widely effective as the honey bee, and with the disease losses among wild and hobbyist honey bees, the commercial honey bees are more important than ever.
For this reason, alternatives have been proposed. Bumble bees (Bombus) are increasingly used in greenhouse cultivation, where a honey bee hive would be too large, e.g., cabbage and carrot for seeds, kiwi fruits, strawberries, summer squash, eggplant and tomatoes for fruit. About a quarter of a million colonies of bumble bees are reared artificially every year, and they are used in over thirty different countries on over twenty-five crops. Hence, bumble bees are of great economic importance, and with the increase of glasshouse cultivation, and the spread of the mite, Varroa jacobsoni, causing a decline in honeybee populations, their importance can only increase. This is in spite of the fact that bumble bees do not produce harvestable quantities of honey, though they do store a small amount to sustain themselves for short periods.
The ability to manipulate the rates and timing of the bee foraging behaviors would be a great advantage to the beekeeper. With continuing pressures on honey bee populations, there is a need to be able to maximize the ability of existing colonies, or alternative species of the bee family, to ensure pollination of crops.
It is therefore an object of the present invention to provide methods and compositions which will aid in directing the foraging behavior of bees, and related methods for use in bee colony management.
The present invention is directed to the identification of synthetic compositions and methods useful in directing foraging activity in bees. Accordingly, the present invention comprises a composition, synthetic brood pheromone, which will influence the behavior of foraging bees. The invention also provides a method for increasing pollen foraging activity in bees, by applying a synthetic brood pheromone comprising methyl palmitate, ethyl palmitate, methyl stearate, ethyl stearate, methyl oleate, ethyl oleate, methyl linoleate, ethyl linoleate, methyl linolenate and ethyl linolenate; or an active mixture comprising one or more of the enumerated esters, to a bee colony to increase the proportion of pollen foragers present in the colony.
A number of different approaches may be used to apply or affix the synthetic brood pheromone to the colony. It is necessary that the bees come into contact with the pheromone, and it is preferred that the pheromone has a reasonable period of time for release within and to the colony. Any such method can be used, so long as the application of the synthetic brood pheromone to the bees results in an increase in the proportion of pollen foragers within the colony.
In one preferred method for utilizing synthetic brood pheromone, colonies are supplied with synthetic brood pheromone, whereby the bees are directed to forage for pollen even when there is no brood in the colony.
In another preferred embodiment, synthetic brood pheromone is used as an aid in bee management, by directing colonies to accumulate extra pollen, which can benefit colonies, i.e., to increase overall nutrition of the colony or to prepare the colony with important pollen stores for over-wintering.
Alternatively, the increase in forager activity may directly benefit the beekeeper or the farmer, by keeping bees in the field collecting pollen longer. This may be a benefit when extending pollination over a long flowering season, to re-initiate pollination for a new crop, or even to initiate pollen foraging activity in time for an early flowering crop. Finally, the beekeeper may benefit if collecting pollen for commercial purposes, by increasing the yield of pollen produced by a hive.
In some cases by extending the bees pollen foraging activity, synthetic brood pheromone will benefit the colony by helping to stabilize the colony, which could be important when establishing a new colony without brood, or to keep a colony together long enough to establish a new queen within the colony. The synthetic brood pheromone reduces the drift of bees away from an establishing or temporary colony. In many applications, such as where a new colony is being established with a new queen, there may be an advantage to additionally applying queen mandibular pheromone to the colony with the synthetic brood pheromone, as the queen mandibular pheromone will further aid in keeping the workers returning to the colony.
In a preferred embodiment, the synthetic brood pheromone is incorporated into a device for insertion into the bee colony.
In a further embodiment of the present invention synthetic brood pheromone is incorporated as part of a xe2x80x9cpollination unitxe2x80x9d, which allows the rapid establishment of a quantity of bees in the field focused on pollination. The simplest version of such a pollination unit includes a collection of bees and a sufficient quantity of synthetic brood pheromone to create a temporarily stable population of bees. Such a unit preferably includes at least about 5,000 bees, and preferably in the range of about 10,000 to 15,000 or more when using honey bees (approximately 3 to 5 pounds of honey bees). In a more preferred embodiment, a quantity of synthetic queen mandibular pheromone is included with the pollination unit.
The pollination unit includes the synthetic brood pheromone, either affixed to the housing or provided in a separate form for application of the synthetic pheromone to the colony.
With such a unit, the responsibility of hive maintenance is dispensed with, and the entire unit may even be disposable, in the sense that the colony can be left in an orchard at the end of the pollination season.
The pollination unit may be supplied with a comb and a quantity of food, such as sugar, for the establishment of the unit. In a preferred embodiment the pollination unit will include a housing unit appropriate for the social activities of the colony of honey bees. For temporary disposable applications, the housing unit will be disposable itself, and preferably of biodegradable materials. In such a case, the manager of an orchard may treat the pollination unit as fully disposable unit, with no need to remove the bees or the housing from the orchard or field at the end of the season. This may be especially advantageous where numerous such units are to be applied to the field or orchard, and where subsequent seasonal activities, such as spraying, may be harmful to a traditional breeding colony. If the pollination unit is disposable, the bees will drift away or die over time, with no brood or queen to permanently link them to the housing unit.
Alternatively, the pollination unit may include a queen, for the establishment of a permanent, breeding colony.